Channel Sounding Using Multiple Sounding Configurations

ABSTRACT

More than one set of sounding signal configuration parameters are determined for the same mobile terminal. The mobile terminal uses the sets of configuration parameters to generate different sounding reference signals which can be used for different purposes such as estimating timing and channel quality. In one embodiment, a method of configuring uplink sounding transmissions by mobile terminals in a wireless communication network is characterized by determining different sets of configuration parameters for sounding signal transmissions for a given mobile terminal ( 200 ). The different sets of configuration parameters are transmitted to the mobile terminal, allowing the mobile terminal to generate different sounding signals for different uses by the wireless communication network ( 202 ).

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/672,324, filed 5 Feb. 2010, which is the National Stage ofInternational Application No. PCT/EP2008/057559, filed 16 Jun. 2008,which claims the benefit of U.S. Provisional Application 60/954,734,filed 8 Aug. 2007, the disclosures of each of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention generally relates to uplink sounding referencesignals, and particularly relates to configuring individual mobileterminals with a plurality of uplink sounding reference signaltransmission parameters.

BACKGROUND

Uplink sounding reference signals are known signals transmitted on theuplink direction (i.e., mobile-terminal-to-network). Sounding referencesignals can be used by the receiver (i.e., the base station) to estimateuplink channel quality, including the uplink channel quality fordifferent frequency bands. The channel quality estimates can, forexample, be used by an uplink scheduler located in the base station todetermine a suitable uplink data rate (i.e., uplink rate control) orselect a suitable frequency band for the uplink transmission for a givenmobile terminal (also known as channel-dependent frequency-domainscheduling).

Uplink sounding reference signals can also be used by the receiver toestimate the timing of received signals. Such receive-timing estimatescan be subsequently used by the network to adjust the mobile terminaltransmit timing in order to time-align the receive timing of the uplinktransmissions of different mobile terminals. Other uses of the uplinksounding reference signals are also possible.

In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution),uplink sounding reference signals can be viewed as OFDM signals(Orthogonal Frequency-Division Multiplexing) in that the signals consistof a number of frequency sub-carriers with suitable modulation appliedto each sub-carrier. More specifically, in case of LTE the modulationapplied to the subcarriers is based on so called Zadoff-Chu sequences.An uplink sounding reference signal can be characterized in thefrequency domain by the index of the first transmitted sub-carrier ofthe reference signal, the number of transmitted sub-carriers of thereference signal and the spacing between transmitted sub-carriers, alsoreferred to as the repetition factor (RPF) of the reference signal.

Uplink sounding reference signals can also be characterized in the timedomain. The LTE uplink time-domain structure includes subframes of 1 mslength. Each subframe has two equal-sized slots of 0.5 ms length, eachslot including seven symbols. One symbol in each slot is used as ademodulation reference signal that cannot be mixed with soundingreference signals. The demodulation reference signals are used foruplink channel estimation to enable coherent uplink detection. Theremaining symbols are typically used for data transmission. Thus, thereare two demodulation reference symbols and twelve “data” symbols withineach subframe.

If sounding reference signals are to be transmitted, a subset of thedata symbols, e.g., every Mth data symbol, can be replaced by soundingreference signals. Typically, sounding reference signals are nottransmitted in every subframe. Instead, one data symbol in every Nthsubframe is replaced by a sounding reference signal, the soundingreference signal including a number of sub-carriers in the frequencydomain as described above. The sounding reference signal can becharacterized in the time domain by the period (measured in number ofsubframes) of the sounding reference signal, i.e., how often thereference signal is transmitted. The sounding reference signal can befurther characterized in the time domain by the time offset of thesounding reference signal (measured in number of subframes) and theposition of the sounding reference signal within the subframe, i.e.,which data symbol has been replaced by the reference signal.

Different uses of uplink sounding reference signals may requiredifferent characteristics for the reference signals. For example, if asounding reference signal is to be used for channel-quality estimation,a sounding reference signal of relatively narrow bandwidth (i.e.,relatively few transmitted sub-carriers) may be sufficient if schedulingis only to be carried out over a limited bandwidth. However, thesounding reference signal is typically transmitted relatively often(i.e., relatively small period) in order to track relatively fastchannel variations. On the other hand, for timing-estimation purposes, arelatively wideband reference signal may be needed to yield an accuratetiming estimation. At the same time, a relatively long reference-signalperiod is sufficient for timing-estimation purposes as the propagationdelay typically varies relatively slowly.

One conventional approach used for both channel-quality estimation andtiming estimation purposes involves transmitting a sounding referencesignal with wide bandwidth and high rate (i.e., small period). However,this conventional approach uses a relatively large amount of radioresources to transmit the sounding reference signal because of the widebandwidth and high rate requirements. As such, fewer uplink symbols areavailable for data transmission. Accordingly, a less radio-resourceintensive solution is desired.

SUMMARY

According to the methods and apparatus disclosed herein, more than oneset of sounding signal configuration parameters are determined for thesame mobile terminal. The configuration parameters may differ in thefrequency-domain and/or the time-domain. The sets of configurationparameter are transmitted to the mobile terminal for use by the terminalin generating different sounding reference signals. Occasionally, morethan one sounding reference signal may be transmitted simultaneouslywhen multiple configurations are used. Priorities may be assigned to thedifferent sets of configuration parameters for mitigating signaltransmission conflicts. The configuration parameter having the highestpriority controls which reference signal is transmitted when a conflictis expected to occur. Sounding reference signals transmitted by themobile terminal can be used for different purposes such as estimatingchannel quality and timing.

In one embodiment, a method of configuring uplink sounding transmissionsby mobile terminals in a wireless communication network is characterizedby determining different sets of configuration parameters for soundingsignal transmissions for a given mobile terminal. The different sets ofconfiguration parameters are transmitted to the mobile terminal,allowing the mobile terminal to generate different sounding signals fordifferent uses by the wireless communication network.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a wireless communicationnetwork including a base station that provides different sounding signalconfigurations for a given mobile terminal.

FIG. 2 is a flow diagram of an embodiment of program logic for providingdifferent sounding signal configurations for a given mobile terminal.

FIG. 3 is a flow diagram of an embodiment of program logic forgenerating different sounding signals by a given mobile terminal basedon different sounding signal configurations.

FIG. 4 is a block diagram of an embodiment of different sounding signalconfigurations for a given mobile terminal.

FIG. 5 is a block diagram of another embodiment of different soundingsignal configurations for a given mobile terminal.

DETAILED DESCRIPTION

FIG. 1 illustrates an embodiment of a wireless communication network 100including a base station 110 that services one or more mobile terminals120. The base station 110 includes a baseband processor 130. A parametergenerator 140 included in or associated with the baseband processor 130determines different sets 150 of configuration parameters for soundingsignal transmissions for the mobile terminal 120, e.g., as illustratedby Step 200 of FIG. 2. The baseband processor 130 transmits thedifferent sets 150 of configuration parameters to the mobile terminal120 over a downlink communication channel 152, e.g., as illustrated byStep 202 of FIG. 2. The sets 150 of configuration parameters enable themobile terminal 120 to generate different sounding signals 160 fordifferent uses by the base station 110 such as channel-qualityestimation and timing estimation.

The mobile terminal 120 has a baseband processor 170 for receiving thesets 150 of configuration parameters transmitted from the base station110, e.g., as illustrated by Step 300 of FIG. 3. A sounding signalgenerator 180 included in or associated with the mobile terminalbaseband processor 170 generates different sounding reference signals160 based on the different sets 150 of configuration parameters, e.g.,as illustrated by Step 302 of FIG. 3. The mobile terminal 120 transmitsthe sounding signals 160 to the base station 110 over an uplinkcommunication link 162. This way, multiple sounding reference signalconfigurations having different frequency-domain and/or time-domainparameters can be used by the same mobile terminal 120 to generatedifferent sounding reference signals 160.

According to one embodiment, one set 150 of the sounding signalconfiguration parameters causes the mobile terminal 120 to generate afirst one of the sounding reference signals 160 with a relatively narrowbandwidth, but high rate in the time domain. A different set 150 of thesounding signal configuration parameters causes the mobile terminal 120to generate a second one of the sounding reference signals 160 having awider bandwidth, but lower time-domain rate. The first sounding signalcan be used by the base station 110 for channel-quality estimation whilethe second sounding signal can be used for timing estimation.

Under some conditions, the different sets 150 of configurationparameters may create signal transmission conflicts at the mobileterminal 120 in that different sounding reference signal transmissionsmay occur within the same subframe or even within the same symbol, e.g.,as illustrated in FIG. 4. Different priorities can be established orotherwise defined for the sets 150 of configuration parameters. Thepriorities allow the mobile terminal baseband processor 170 to determinewhich set 150 of configuration parameters should be used in the event ofa sounding signal transmission collision. The configuration having thehighest priority controls when more than one sounding reference signaltransmission is expected to occur simultaneously, e.g., as illustratedin FIG. 5 where the second configuration (#2) has the highest priority.The prioritization may be explicit such that each sounding referencesignal configuration is explicitly assigned a priority at configuration.Alternatively, the prioritization can be implicit, e.g., depending onthe different configuration parameters. According to one embodiment, theconfiguration having the widest bandwidth (consisting of the largestnumber of transmitted sub-carriers) is given the highest priority. Otherimplied priorities may also be implemented by the mobile terminalbaseband processor 170.

The embodiments described herein provide for the configuration, use andtransmission of multiple sounding reference signal configurations to thesame mobile terminal 120. The configurations may differ in bandwidthand/or the number of transmitted frequency sub-carriers. Additionally,or alternatively, the configurations may differ in the spacing betweenthe transmitted sub-carriers (i.e. in the repetition factor), and/or insignal transmission rate. Additionally, or alternatively, theconfigurations may have different explicit or implied priorities foravoiding conflicting sounding reference signal transmissions expected tooccur simultaneously (or just in the same sub-frame). In one embodiment,the base station 110 explicitly signals the configuration priorities tothe mobile terminal 120.

Of course, other variations are contemplated. Thus, the foregoingdescription and the accompanying drawings represent non-limitingexamples of the methods and apparatus taught herein for the transmissionof system information. As such, the present invention is not limited bythe foregoing description and accompanying drawings. Instead, thepresent invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. A method of configuring uplink soundingtransmissions by mobile terminals in a wireless communication network,the method comprising: determining different sets of configurationparameters for sounding signal transmissions for a given mobileterminal; and transmitting the different sets of configurationparameters to the mobile terminal, thereby enabling the mobile terminalto generate different sounding signals for different uses by thewireless communication network.
 2. The method of claim 1, whereindetermining different sets of configuration parameters includesdetermining a first sounding signal bandwidth parameter for a first setof configuration parameters and a second sounding signal bandwidthparameter for a second set of configuration parameters, such that themobile terminal can generate a relatively narrowband sounding signalaccording to the first set of configuration parameters and generate arelatively wideband sounding signal according to the second set ofconfiguration parameters.
 3. The method of claim 2, wherein the firstand second sounding signal bandwidth parameters including transmissionfrequency parameters, and configuring the transmission frequencyparameters such that the mobile terminal transmits the relativelynarrowband sounding signal more frequently than it transmits therelatively wideband sounding signal.
 4. The method of claim 1, furthercomprising establishing or otherwise defining different priorities forthe different sets of configuration parameters, thereby allowing themobile terminal to determine which set of configuration parametersshould be used if a sounding signal transmission conflict occurs.
 5. Themethod of claim 4, further comprising the mobile terminal configured totransmit a first sounding signal at first times according to a first setof configuration parameters and a second sounding signal at second timesaccording a second set of configuration parameters, and establishing orotherwise defining priorities for the different sets of configurationparameters comprises establishing or otherwise defining whether thefirst or second sounding signal is to be transmitted for a case wherethe first and second times coincide.
 6. The method of claim 4, furthercomprising transmitting the different priorities from the wirelesscommunication network to the mobile terminal.
 7. A base stationcomprising a baseband processor configured to: determine different setsof configuration parameters for sounding signal transmissions for agiven mobile terminal; and transmit the different sets of configurationparameters to the mobile terminal, thereby enabling the mobile terminalto generate different sounding signals for different uses by the basestation.
 8. The base station of claim 7, wherein the baseband processoris configured to determine a first sounding signal bandwidth parameterfor a first set of configuration parameters and a second sounding signalbandwidth parameter for a second set of configuration parameters, suchthat the mobile terminal can generate a relatively narrowband soundingsignal according to the first set of configuration parameters andgenerate a relatively wideband sounding signal according to the secondset of configuration parameters.
 9. The base station of claim 8, whereinthe first and second sounding signal bandwidth parameters includingtransmission frequency parameters, and the baseband processor isconfigured to set the transmission frequency parameters such that themobile terminal transmits the relatively narrowband sounding signal morefrequently than it transmits the relatively wideband sounding signal.10. The base station of claim 7, wherein the baseband processor isfurther configured to establish or otherwise define different prioritiesfor the different sets of configuration parameters, thereby allowing themobile terminal to determine which set of configuration parametersshould be used if a sounding signal transmission conflict occurs. 11.The base station of claim 10, wherein the baseband processor isconfigured to establish first sounding signal transmission times for afirst set of configuration parameters and second sounding signaltransmission times for a second set of configuration parameters, and toestablish or otherwise define whether the first or second set ofconfiguration parameters has a higher priority when the first and secondsounding signal transmission times coincide.
 12. The base station ofclaim 11, wherein the baseband processor is further configured totransmit the different priorities to the mobile terminal.
 13. A methodof configuring uplink sounding transmissions by a given mobile terminal,the method comprising: receiving different sets of configurationparameters for sounding signal transmissions for the mobile terminal;and generating different sounding signals by the mobile terminal basedon the different sets of configuration parameters.
 14. The method ofclaim 13, wherein receiving different sets of configuration parametersincludes receiving a first sounding signal bandwidth parameter for afirst set of configuration parameters and a second sounding signalbandwidth parameter for a second set of configuration parameters. 15.The method of claim 14, further comprising: generating a relativelynarrowband sounding signal according to the first set of configurationparameters; and generating a relatively wideband sounding signalaccording to the second set of configuration parameters.
 16. The methodof claim 15, wherein the relatively narrowband sounding signal isgenerated more frequently than the relatively wideband sounding signal.17. The method of claim 13, further comprising determining which set ofconfiguration parameters should be used when a sounding signaltransmission conflict occurs.
 18. The method of claim 17, whereindetermining which set of configuration parameters should be used isbased on different received priorities for the different sets ofconfiguration parameters.
 19. A mobile terminal comprising a basebandprocessor configured to: receive different sets of configurationparameters for sounding signal transmissions for the mobile terminal;and generate different sounding signals based on the different sets ofconfiguration parameters.
 20. The mobile terminal of claim 19, whereinthe baseband processor is configured to receive a first sounding signalbandwidth parameter for a first set of configuration parameters and asecond sounding signal bandwidth parameter for a second set ofconfiguration parameters.
 21. The mobile terminal of claim 20, whereinthe baseband processor is further configured to: generate a relativelynarrowband sounding signal according to the first set of configurationparameters; and generate a relatively wideband sounding signal accordingto the second set of configuration parameters.
 22. The mobile terminalof claim 21, wherein the baseband processor is further configured togenerate the relatively narrowband sounding signal more frequently thanthe relatively wideband sounding signal.
 23. The mobile terminal ofclaim 19, wherein the baseband processor is further configured todetermine which set of configuration parameters should be used when asounding signal transmission conflict occurs.
 24. The mobile terminal ofclaim 23, wherein the baseband processor is further configured todetermine which set of configuration parameters should be used based ondifferent received priorities for the different sets of configurationparameters.